In:
ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2014-02, No. 21 ( 2014-08-05), p. 1274-1274
Abstract:
Polymer electrolyte fuel cells (PEFCs) have expected as one of the key energy devices in future sustainable society. PEFCs, however, have difficult issues such as insufficient oxygen reduction reaction (ORR) activity and expensive Pt consumption. To overcome such difficulties, various non-platinum ORR catalysts, such as, carbide, nitride, and oxide were examined as alternative of Pt [1]. Among them, Zr oxide-based catalysts attract much attention. Such transition-metal-oxide catalysts show the high ORR onset potentials, but ORR current is very low. Thus, identifying the ORR sites, and designing surface structure to have effective ORR sites, is mail issues in developing oxide-base catalysts. Previously, we reported that oxygen-vacancy sites could be ORR sites by surface-sensitive conversion-electron-yield x-ray absorption spectroscopy (CEY-XAS) [2]. But we still lack detailed information on preferable electronic structure of oxide-base ORR catalyst. Since carbon is deposited at catalysts surface during partial oxidation preparation processes, conventional laboratory XPS does not provide effective information, especially at valence band (V.B.) region. Thus, we conducted highly brilliant soft X-ray synchrotron radiation (SR)-XPS measurements. First-principles calculation was adopted to interpret the partial density of state (PDOS) of V. B. ZrO 2 based catalyst samples were prepared under O 2 and H 2 /N 2 atmosphere from Zr- phthalocyanine. The SR-XPS measurements were performed on BL-18A beam line at Photon Factory (PF) of High Energy Accelerator Research Organization (KEK). PDOS calculation was carried out by using the plane-wave basis projected augmented wave (PAW) method (VASP) [3]. Figure 1 (a) shows the soft x-ray SR-XPS spectra of ZrO 2 reference. Each spectrum was obtained after subtracting the spectrum measured at 31 eV X-ray energy. We can see that peak intensity at 4 to 8 eV regions were increased as incident energy increased, suggesting that these peaks originate from ZrO 2 . As shown in Fig.1 (b), the SR-XPS spectra of ZrO 2 catalyst also show similar trend. This indicates that we can truly observe V.B of catalysts even if a part of surface is covered with carbon. Figure 2 shows the PDOS spectra calculated ZrO 2 with oxygen vacancy. The Peak near 4eV can be originated from O 2p. This result suggest reduction of SR-XPS spectral intensity for catalysts compared with reference ZrO 2 comes from oxygen vacancy in the catalysts, and such O-vacancy should play a role in emergence of ORR activity. Detailed electronic structure consideration will be presented at Meeting. Acknowledgement: A part of this work was performed under the “Non-precious metal oxide-based cathode for PEFC Project” supported by the New Energy and Industrial Technology Development Organization (NEDO). SR-XPS measurements were performed with an approval of High Energy Accelerator Research Organization (Proposal No. 2013P102) . References: [1] A. Ishihara, Y. Shibata, S. Mitsushima, K. Ota, J.Electrochem. Soc., 155, B400-B406 (2008). [2] H. Imai, M. Matsumoto, T. Miyazaki, S. Fujieda, A. Ishihara, M. Tamura, and K. Ota, Appl. Phys. Lett. 96, 191905 (2010). [3] G. Kresse and J. Furthmuller, Phys. Rev. B, 54, 11169 (1996).
Type of Medium:
Online Resource
ISSN:
2151-2043
DOI:
10.1149/MA2014-02/21/1274
Language:
Unknown
Publisher:
The Electrochemical Society
Publication Date:
2014
detail.hit.zdb_id:
2438749-6
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